1. Field of the Invention
The present invention relates to a motor control device for controlling a multi-phase motor including a plurality of sets of windings, a current control method applied to a motor control device, and an electric power steering device using a motor control device.
2. Description of the Related Art
As a motor control device for controlling a conventional multi-phase motor including a plurality of sets of windings, there is a motor control device having a configuration in which a motor includes two sets of windings, and the motor control device includes two inverters for controlling currents flowing through the respective sets of windings, thereby independently controlling the currents (for example, refer to Japanese Patent Application Laid-open No. 2011-131860).
The motor control device according to Japanese Patent Application Laid-open No. 2011-131860 includes, in order to supply respective inverters with power from a power supply, power supply relays for electrical connection/disconnection. When a failure occurs on a winding or an inverter on one side, the motor control device opens a power supply relay for the side on which the failure has occurred, thereby interrupting the connection to the power supply. The motor control device also controls the inverter on the normal side, thereby continuing an output of torque from the motor.
However, the conventional technology has the following problems.
In the example described in Japanese Patent Application Laid-open No. 2011-131860, a power supply relay connected to a failed inverter out of the plurality of inverters is opened. However, when a short-circuit failure occurs, a closed circuit through a portion of the short-circuit failure and a windings is formed, resulting in a circulating current that does not flow through the power supply. Then, this circulating current generates a torque acting in a direction of decelerating the rotation of the motor, namely a brake torque is generated. This brake torque is generated by a current that does not flow through the power supply, and cannot be restrained only by opening the power supply relay. Accordingly, there occurs a problem of a lack of torque.
Moreover, an advantage of opening a power supply relay on a failed side is that it is possible to prevent excessive heat generation and current consumption in the following case. That is, assume a case where a short-circuit failure of a switching element or a failure of ground fault or power-supply fault of an inverter or a winding occurs, and after a power supply relay on a failed side is opened, in a connection state in which the power supply relay on the failed side is not opened, a secondary failure further occurs in a pair of a winding and an inverter (hereinafter, also referred to as winding drive system) on the failed side, and the secondary failure is a short-circuit failure of the winding drive system.
In this case, via the two locations of the primary failure and the secondary failure, the positive electric potential and the negative electric potential of the power supply become a state close to a short circuit, which may lead to a state in which an excessive current is generated. As a result, excessive heat generation and current consumption possibly occur. Then, one method of providing an advantage of preventing this state from occurring is the method of opening the power supply relay on the failed side when a primary failure occurs, namely the method according to Japanese Patent Application Laid-open No. 2011-131860.
However, this method requires as many power supply relays as the number of the plurality of winding drive systems, and there is a problem of an increase in price of the device.